[mythtv-users] OT: LED or Plasma (was Advice on choosing a TV)

Paul Gardiner lists at glidos.net
Thu May 27 22:44:33 UTC 2010

Indulis Bernsteins wrote:
>  > Are you seeing a lot of posterization from yours in darker images,
>  > especially on walls and faces? At first I thought it was just the
>  > TV being larger than I was used to showing up poor sources, but
>  > I'm seeing it in all sources. Also, if I pause and adjust the
>  > brightness, the colour bands move, which also indicates that it's
>  > the TV not the source. It's bad enough that I'm considering
>  > returning it. Although maybe this is a problem with all modern
>  > TVs.
>  > Paul.
> Paul,
> I think this is normal.  I am trying to remember where I saw a really 
> good discussion about this in the last few weeks.
> If you imagine the input is 256 levels, and your brightness and contrast 
> settings "crunch" these into 170 levels on the actual display (say the 
> bottom 40 levels of input all translate to output of 0 or dead black), 
> then with a full range of input levels (say a blue sky or the blue 
> Mythtv theme!) you'll get adjacent input levels the picture moving in 
> between the 170 levels (1 level of input change "clicks over" 2 or 3 
> levels of output), and you'll see the "bands" move.
> Say
>   input 50 = output 75 due to your brightness/contrast settings
>   and input 51 = output 78
> but if you change contrast/brightness a bit,
>   input 50 might = 78
>   and input 51 also = 78
> so the "bands" between the colours move around.  I have probably done a 
> cr at p job of explaining this!

Yes, I guess my reasoning was a bit simplistic. I was thinking if the
banding was all in the source, and the TV was perfect then changing
the brightness wouldn't move the bands. Hence, since the bands do move
then the TV isn't perfect. I think that's true, but we know TVs aren't
perfect so the argument doesn't tell us much.

I think I see what you are saying: so the source has banding and then 
the TV is making some of adjacent bands coalesce to make wider bands.

> You will find the high contrast "demo" or "vivid" settings on a TV do a 
> LOT of crunching of the video data into a small subset of levels, so the 
> quantisation becomes more apparent- the banding is worse.  You lose 
> definition in shadows and fine detail for the same reason.

I've been using the TV's THX setting. The other setting look to overblown.

> The best I can suggest, is to get a copy of the Digital Video Essentials 
> (DVE) DVD or Blueray.  Use it to set up the right brightness and 
> contrast settings for your TV.  If you have Terminator 2 on DVD, it and 
> some others have a short version of the Digital Video Essentials type of 
> guided setup ("THX setup menu").
> Often video rental stores have a copy of DVE you can rent for a day, but 
> I think it is good to have one around all the time.

I have a copy. :-) I haven't had a chance to try it out yet. One problem
though: I have a blu-ray version of DVE. I was assuming I could
calibrate using my blu-ray player and then use the settings for all
sources, but now I have my new ION board working, I'm finding the
brightness levels from MythTv much different to everything else. Dark
areas are much darker. I'm surprised. I thought HDMI was a digital
connection so there'd be no difference. I'll either need to find out
what's causing the difference and rectify it, or find a way to play
the calibration disc through MythTv.

> You may also be seeing two different effects- one is posterisation from 
> lousy overcompressed sources, the other is the bands moving when you 
> adjust brightness.contrast, the two are not necessarily related, so you 
> can't draw the conclusion it is just the TV.  Personally I think you're 
> seeing two different things.
> If you can find a very good video source (good progressive scan DVD 
> player- pioneer, Sony, Oppo, try looking at "secrets of home theater" 
> http://www.hometheaterhifi.com/ which has a lost of good progressive 
> scan DVD players.. and there is a lot of difference even between a $80 
> and a $150 player with progressive scan) and a good DVD disc (check 
> avsforum for examples of good test discs, some of the animation films 
> from Pixar are v good, and if you can score a "superbit" DVD on eBay, 
> these were DVDs with no extras and remastered for the maximum amount of 
> just film video+audio data that could squeeze onto a DVD).

That's another thing I don't really understand, how there can be much
difference between blu-ray players when its all digital, and there is
no format conversion. I guess they might use different accuracy DCTs.

I have a player - the Sony BDP-S370. That was one of the things that
worried me about the TV. Even with a blu-ray disc I see a little
banding, and faces don't look as natural as with my old CRT.
Hopefully calibration will make a differnce.


More information about the mythtv-users mailing list